1. We have employed T cell clones specific for a syngeneic murine leukemia in models of adoptive immunotherapy. We demonstrated that cytotoxic T cell clones, activated with antigen to induce IL-2 receptor expression, were extremely effective in mediating anti-tumor responses when administered in conjunction with systemic interleukin-2. More recently we have shown that non-cytotoxic inducer T cell clones also demonstrate significant anti-tumor activity in vivo. 2. We have performed experiments to assess the capacity of lectin (Con A), ionomycin, phorbol ester (PMA) and recombinant IL2 to mediate proliferation as well as the expression of cell-surface IL2 receptors, two lymphokine genes, IL2 and IFN-Gamma, and the c-myc proto-oncogene in cloned T cell populations. Stimulation of T cell clones with recombinant IL2 resulted in proliferation and sustained expression of the c-myc cellular proto-oncogene, but did not induce the expression of mRNA for the lymphokines IFN- and IL2. In contrast, stimulation of cloned T cells with lectin alone induced significant IFN- and IL2 mRNA expression, up-regulation of the number of cell surface IL2 receptors and transient c-myc mRNA expression. Ionomycin alone was not a sufficient signal for lymphokine mRNA induction. The phorbol ester PMA alone induced neither proliferation nor lymphokine gene expression but potentiated lectin and ionomycin-mediated signals.